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Glycyrrhiza glabra

English: Liquorice

Hindi: Mulethi

Sanskrit: Yashtimadhu, madhuka

The name 'glycyrrhiza' was coined by Oioscorides in the first century, by combining the Greek words glukos meaning sweet and rhiza meaning root. Theophrastus also referred to it as Radix Oulcis from the Latin equivalent. Liquorice has been used for centuries to treat various ailments throughout Europe and Asia; Pliny (23 AD) and Hippocrates (400 BC) both described the use of the plant. In Ayurveda it is considered to be a rasayana and is an important ingredient of many formulae, especially for bronchial conditions. Western herbalists use it for ulcers, as an antiinflammatory and expectorant and the Chinese ascribe rejuvenative and aphrodisiac powers to liquorice.

Habitat

It is a native of the Mediterranean region and the Near East and can now be found throughout the subtropical and temperate regions of the world. Liquorice is cultivated throughout Russia, Turkey, Greece, the Middle East, China and most of Asia and Europe and is readily commercially available as transversely cut pieces of root.

Botanical description

G. glabra is a hardy perennial shrub, attaining a height up to 2.5 m (Plate 31). The leaves are compound, imparipinnate, alternate, having 4-7 pairs of oblong, elliptical or lanceolate leaflets. The flowers are narrow, typically papilionaceous, borne in axillary spikes, lavender to violet in colour. The calyx is short, campanulate, with lanceolate tips and bearing glandular hairs. The fruit is a compressed legume or pod, up to 1.5 cm long, erect, glabrous, somewhat reticulately pitted, and usually contains 3-5 brown, reniform seeds. The taproot is approximately 1.5 cm long and subdivides into 3-5 subsidiary roots, about 1.25 cm long, from which the horizontal woody stolons arise. These may reach 8 m and when dried and cut, together with the root, constitute commercial liquorice. It may be found peeled or unpeeled. The pieces of root break with a fibrous fracture, revealing the yellowish interior with a characteristic odour and sweet taste.

Parts used

Dried roots and stolons, peeled or unpeeled.

Traditional and modern use

It is used as a tonic, laxative, demulcent, expectorant and emollient in many traditional systems of medicine. It finds particular use in cough, catarrh, bronchitis, fever, gastritis, gastric and duodenal ulcers and skin diseases and as a general tonic. It has been applied externally to cuts and wounds and used in the treatment of hyperdipsia, genitourinary diseases and many other minor indications, including as a corticosteroid replacement agent.

Ethnoveterinary usage

In India, Glycyrrhiza glabra has been used extensively for the treatment of various ailments of domestic animals from ancient times, for similar purposes to those in humans. For example, it is used for coughs and colds, as an expectorant and wound-healing agent in ruminants.

Major chemical constituents

Triterpene saponins

Glycyrrhizin (glycyrrhizic acid) is the major saponin, responsible for the sweet taste of liquorice, and its aglycone, glycyrrhetinic acid; together with other derivatives and glycosides such as glycyrrhizol, glabrins A and B, glycyrrhetol, glabrolide, isoglabrolide and others.

Flavonoids and isoflavonoids

Liquiritin, which during drying and storage undergoes partial conversion to isoliquiritin; their aglycones, liquiritigenin and isoliquiritigenin, isolicoflavonol, licoagrodione, glucoliquiritin apioside, prenyllicoflavone A, shinflavone, shinpterocarpin, I-methoxyphyaseollin and rhamnoliquirilin. A variety of isoflavones are also reported form the plant, including formononetin, glabrene, neoliquiritin, hispaglabridin A and B, glabridin, glabrol, 3-hydroxyglarol, glycyrrhisflavone, 4-0-methylglabridin, 3' -hydroxy-4' -0-methylglabridin and many 2-methyl isoflavones.

Phytosterols

Volatile oil

Liquorice contains a trace amount (0,5%) of volatile oil, containing anethole, estragole, eugenol and hexanoic acid as the main constituents.

Medicinal and pharmacological activities

Antiulcer activity: Liquorice has a well-documented antiulcer action, being as effective as cimetidine and pirenzapine in curing peptic ulcer. An Ayurvedic preparation containing liquorice increased ?-glucuronidase activity in the Brunner's glands, offering protection against duodenal ulcer.

Hepatoprotedive activity: Liquorice is used traditionally for the prevention of liver diseases. Administration to experimental animals increased the duration of the lag phase of ascorbate free radical oxidation in the liver and myocardium, the antioxidant activity of the root powder being comparable to that of I)-carotene, and markedly decreased lipid peroxides in liver. An alcoholic extract increased the cumulative biliary and urinary excretion of acetaminophen without affecting the thioether or sulphate conjugates and also increased glucuronidation in rats, suggesting it may intluence detoxification of xenobiotics.

Antioxidant adivity: An investigation using the isotlavonoids of liquorice focused on their ability to protect the liver mitochondria against oxidative stresses. This effect was linked with the inhibition of mitochondrial lipid peroxidation-related respiratory electron transport. Glabridin and its derivatives contributed to the antioxidant activity induced by heavy metal ions and macrophages against low density lipoprotein (LDL) oxidation. LDL oxidation is a major factor in the production aetiology of early arteriosclerosis. The isotlavans also showed a potent scavenging effect on the DPPH radical and were able to chelate heavy metals. This action was associated with the hydroxy functional group as well as the hydrophobic moiety of the isotlavans. Glabridin also inhibited the susceptibility ofLDL to oxidation in an atherosclerotic apolipoprotein E deficient and in vitro human LDL oxidation model and prevented the consumption of I)-carotene and lycopene. Further experiments with glabridin and accompanying isotlavans suggested that glabridin is a potent inhibitor of cholesterollinoleate hydroperoxide formation.

Anticancer adivity: Liquorice potentiated the antitumour and antimetastatic activity of cyclophosphamide when tested in . metastasising Lewis lung carcinoma. Extracts have been assayed for cytotoxicity in vitro using the Yoshida ascites sarcoma; the petroleum ether extract exhibited a more potent activity than other solvent extracts. Liquorice has also been shown to protect against skin tumorigenesis caused by DMBA (7,12-dimethyl-benz [a] anthracene) initiation and 12-0-tetradecanoylphorbol-13-acetate (TPA) promotion. The latency period of tumour onset was increased and the number of tumours decreased, possibly by inhibiting the carcinogen metabolism after DNA adduct formation.

Safety profile

Liquorice is considered safe within the designated therapeutic dosage. Excessive consumption may lead to hypertension and the potentiation of diuretic and corticosteroid activity. Its use in cardiovascular and renal patients is contraindicated as it may lead to disturbance of electrolytic balance and increased sensitivity to cardiac glycosides due to excess excretion of potassium. Use during breastfeeding is also not recommended.